Atlantic halibut are the largest flatfish and one of the most challenging species to farm, with welfare issues centering on stress sensitivity, light requirements, and the difficulties of early life stage management.
Atlantic halibut aquaculture presents welfare challenges at every life stage. Larvae are extraordinarily sensitive — small fluctuations in temperature, salinity, or light regime cause mass mortality events and developmental abnormalities. The metamorphosis from pelagic larvae to bottom-dwelling juveniles is a critical period during which inadequate substrate, inappropriate lighting, or poor nutrition causes permanent malformations affecting swimming, feeding, and survival. Adult halibut crowded in tanks show clear behavioral stress indicators and reduced feed uptake. As benthic animals, they require substrate or resting surfaces in tank systems — suspension in open water without resting areas prevents natural resting posture and causes chronic stress. Pre-slaughter stunning is used in some Norwegian operations but is not universal. Given halibut's longevity and growth potential, welfare conditions during the 3-5 years of production have prolonged impact on individual fish.